Oversampling digital receiver for radio-frequency signals

ABSTRACT

A system and method for receiving a radio frequency signal, comprising a device for digitizing, without prior alteration of frequency, an analog radio frequency representation of each of a plurality of radio frequency signals to produce a respective plurality of digital radio frequency signals having a respective associated radio frequency digital clock, the plurality of digital radio frequency signals having a sufficiently high respective associated clock rate to preserve an information content of an information communication present in the analog radio frequency representation; a switch matrix adapted to concurrently switch the plurality of digital radio frequency signals and associated digital radio frequency clock to ones of a plurality of digital signal processors; and a control adapted to selectively automatically control the concurrent switching of a plurality of digital signals and associated digital clock to the respective plurality of digital signal processors; wherein the digital signal processors produce processed representations of information contained in respective analog radio frequency representations.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.11/966,897, filed Dec. 28, 2007, now U.S. Pat. No. 8,462,889, issuedJun. 11, 2013, and is a Continuation of U.S. patent application Ser. No.11/966,906, filed Dec. 28, 2007, now Pending, which are eachContinuations-in-Part of: U.S. patent application Ser. No. 11/243,019,filed Oct. 4, 2005, now U.S. Pat. No. 7,680,474, issued Mar. 16, 2010;and U.S. patent application Ser. No. 11/243,020, filed Oct. 4, 2005, nowU.S. Pat. No. 7,508,230, issued Mar. 24, 2009; and U.S. patentapplication Ser. No. 11/243,022, filed Oct. 4, 2005, now Abandoned; andU.S. patent application Ser. No. 11/424,121, filed Jun. 14, 2006, nowU.S. Pat. No. 7,362,125, issued Apr. 22, 2008; and U.S. patentapplication Ser. No. 11/360,749, filed Feb. 23, 2006, now U.S. Pat. No.7,443,719, issued Oct. 28, 2008, each of which is expressly incorporatedherein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of switching circuits and, moreparticularly, for switching circuits for advanced digital radioreceivers and transmitters.

2. Description of the Prior Art

A simple classic radio receiver consists of a single antenna coupled toa downconverter that extracts a single “baseband” channel. In a modernreceiver, the baseband signal is digitized with an analog-to-digitalconverter (ADC) and further processed in the digital domain. A classictransmitter contains essentially the same components working in thereverse direction; a transceiver contains both a transmitter and areceiver packaged together.

A multi-band, multi-channel RF communications system (see FIG. 1 a) caninclude multiple antennas, and can extract multiple baseband channels orgroups of channels simultaneously. This requires a switch matrix, whichpermits distribution of various signals between each antenna(corresponding to each band) and one or more appropriate radio receiverchannels. If the system is to be flexible and reconfigurable, it shouldbe possible to redirect input signals to selected output channels.

The signal at the antenna is an analog waveform, even if it may beencoding a digital signal. In a conventional receiver system of theprior art, as illustrated in FIG. 1 a, both the switch matrix and thechannelizing receivers are analog components, and similarly for thetransmitter. However, these band-specific precision analog componentsare often expensive and limited in their flexibility andreconfigurability. Furthermore, these analog switching systems havesevere deficiencies in terms of losses, isolation, crosstalk, andability to multicast.

For these reasons, the communications industry would like to move towardan approach known as “software-defined radio” (SDR) or “software radio”,where all data processing is carried out in the digital domain, exceptright at the antenna itself. This requires ultrafast data converters,with sampling rates of tens of GHz and excellent linearity. ADCs withthe requisite properties have recently been demonstrated, based onsuperconductor electronics using Josephson junctions, with circuitdesigns based on rapid-single-flux-quantum logic (RSFQ). It is naturalthat this data conversion be carried out right at the antenna, asillustrated in FIG. 1 b. But in this case, the switching must also becarried out directly on the digital-RF signals. Furthermore, theprecision and linearity of these signals can be maintained in thedistribution network only if the sampling clock is distributed alongwith the data bits. This requires a new type of digital-RF switchmatrix, which has not been reported before, and which is the subject ofthe present invention.

Furthermore, the digital-RF transceiver architecture allows naturalpartitioning between band-specific (analog) and band-independent(digital) components. Analog components, such as antennas and amplifiersare optimized for performance within a particular frequency band. Evendata converters between analog and digital formats, ADCs and DACs, workbest with designs that target specific frequency bands. Furthermore, anADC or DAC optimized for a particular frequency band will typically havea particular sampling frequency (clock frequency f_(clock)) that ispreferred for best performance. For example, a radio-frequency bandpassADC designed for a center frequency f) may exhibit the greatest dynamicrange for a sampling frequency that is four times the center frequency(f_(clock)=4×f)). On the contrary, digital signal processing units,operating on numbers, are independent of the signal characteristics.This partitioning enables the true software radio paradigm by allowingfull software programmability of the RF distribution network.Superconductor electronics are fast enough to digitize at multi-GHz RFand perform subsequent processing completely in the digital domain.

Switch matrices based on superconducting electronic circuits have beenrecently reported by several inventors. For example, see (1) U.S. Pat.No. 6,960,929, issued Nov. 1, 2005 by inventor Fernand D. Bedard,entitled Superconductive Crossbar Switch, (2) U.S. Pat. No. 6,917,537,issued Jul. 12, 2005 by inventor Paul I. Bunyk entitled RSFQBatcher-Banyan Switching Network, (3) U.S. Pat. No. 6,865,639, issuedMar. 8, 2005 by inventor Quentin P. Herr entitled Scalable Self-RoutingSuperconductor Switch, and (4) Hashimoto et al., Implementation of a 4×4Switch With Passive Interconnects, IEEE Trans. Appl. Supercon., vol 15,no. 2, June 2005, pp. 356-359.

However, none of these patents was designed for an application in RFcommunications, and none of these include switches which route the clocksignal together with the data signal, which are two of several reasonsthis invention distinguishes over the prior art. See also the article byD. K. Brock, O. A. Mukhanov, and J. Rosa, “Superconductor DigitalDevelopment for Software Radio,” IEEE Commun. Mag., pp. 174-179,February 2001, and K. K. Likharev and V. K. Semenov, “RSFQ Logic/MemoryFamily: A new Josephson junction technology for sub-THz digitalsystems”, IEEE Trans. Appl. Supercond., vol. 1, pp. 3-28, 1991.

Problems of the Prior Art

The prior art switches have been expensive and limited in theirflexibility and ability to reconfigure. In addition, they have severedeficiencies in terms of losses, isolation, cross talk and ability tomulticast.

It is natural and desirable that data conversion be carried out right atthe antenna, but, in such a case, the switching must also be carried outdirectly on the digital-RF signals. Further, the precision and linearityof these signals can be maintained in the distribution network only ifthe sampling clock is distributed along with the data bits. Thisrequires and new type of digital-RF switch matrix which is the subjectof the present invention.

Summary and Objects of the Invention

A multi-carrier, multi-channel RF communication system requires a switchmatrix to route various signals between a set of antennas and a set ofradio transceivers. This can be carried out most efficiently in thedigital domain, but requires the use of ultrafast circuits that canaccurately process multi-GHz RF signals.

One aspect of the invention is directed to a switch matrix which issuitable for routing various signals between a set of antennas and a setof radio transceivers. The transceivers can be multi-carrier,multi-channel RF communication devices. The routing is carried out inthe digital domain and uses ultra fast superconductive circuits that canaccurately process multi-gigahertz RF signals. For best performance thebasic switching cell must carry both the data bits and the samplingclock, where the sampling clock may be at different frequencies forsignals from different RF bands distributed within the same switchmatrix.

Preferred exemplary embodiments of the invention are implemented usingultra fast RSFQ superconducting logic elements.

It is therefore an object of the invention to provide a method forreceiving a radio frequency signal, comprising digitizing, without prioralteration of frequency, an analog radio frequency representation ofeach of a plurality of radio frequency signals to produce a respectiveplurality of digital radio frequency signals having a respectiveassociated radio frequency digital clock, the plurality of digital radiofrequency signals having a sufficiently high respective associated clockrate to preserve an information content of an information communicationpresent in the analog radio frequency representation; concurrentlyswitching the plurality of digital radio frequency signals andassociated digital radio frequency clock to ones of a plurality ofdigital signal processors; selectively automatically controlling theconcurrent switching of a plurality of digital signals and associateddigital clock to the respective plurality of digital signal processors;and producing, by the digital signal processors, processedrepresentations of information contained in respective analog radiofrequency representations.

The associated radio frequency clock for at least two of the respectivedigital radio frequency signals may be independent of each other.

At least one associated radio frequency digital clock may have a clockrate above a Nyquist rate for a radio frequency carrier of the analogradio frequency representation. Thus, the analog to digital convertermay operate at frequencies in excess of 350 mega-samples per second,and, for example, at frequencies of 1, 5, 10, 20, 40 or even 100giga-samples per second, with corresponding clock frequencies of 1, 5,10, 20, 40, 100 GHz, or higher. Typically, the preferred oversamplingrange is at least 4 times the highest substantial-power frequencycomponent in the band to be subsequently analyzed. Because there is noparticular requirement for down-conversion or frequency translation ofthe signals, the band may be a “baseband” signal, that is, one in whichenergy components extend to DC or near 0 Hertz. Practically, a receivedradio frequency signal will not have such low frequencies, but in somecases may include signals in the kilohertz or higher range. Each analogsignal coupler may therefore be adapted to couple a radio frequencysignal within a band, the band having an upper range limit, theassociated clock for the respective analog to digital converteroperating above a Nyquist rate for the upper range limit.

As is known, if the frequency of a signal component having significantpower exceeds the Nyquist rate, which is considered double the highestfrequency, then there will be aliasing of the signal onto lowerfrequency components. While this is generally undesirable, in somecases, it is acceptable, especially where the signal has a frequencyabove the capabilities of the process, it has modulated information thatcan be extracted from the aliased signal, and when aliased, it does notinterfere with reception of a signal of interest. Each analog signalcoupler may therefore be adapted to couple a radio frequency signalwithin a band, the radio frequency signal comprising an informationsignal, the associated clock for the respective analog to digitalconverter operating above a minimum rate required to capture anddigitally represent the information signal from the radio frequencysignal.

At least two digital signal processors may be concurrently switched toprocess a respective digital radio frequency signal.

At least one of the respective digital radio frequency signals maycomprises a parallel multiple binary bit digital representation of therepresentation of the analog radio frequency representation. At leastone of the respective analog to digital converters may generate aparallel multiple binary bit digital representation of therepresentation of the radio frequency signal, the parallel multiplebinary bit digital representation and associated clock being routed bythe non-blocking switch matrix to at least one digital radio frequencysignal processor. The multiple binary bit analog-to-digital convertermay be, for example, a single bit delta-sigma architecture converter,which is processed to produce a multi-bit output, or an intrinsicallymultibit converter. Of course, a single bit converter and signaldistribution architecture may also be employed.

A delay of a digital radio frequency signal and respective associatedradio frequency digital clock may be matched to maintainsynchronization. A delay of a digital radio frequency signal may beselectively controlled. At least two of the associated radio frequencydigital clocks having different frequencies may be generated. Aswitching may occur to change an analog radio frequency representationrouted to a digital signal processor dynamically in real time.

The plurality of analog radio frequency representations are receivedthrough respective separate antennas. At least two of the analog radiofrequency representations may be in the same or different radiofrequency bands, or in overlapping bands. If in the same or overlappingband, these signals may be, for example, subject to differentdigitization processing and/or analog or digital processing. Preferably,analog processing is minimized, to thereby eliminate sources of analoglinear and non-linear distortion.

At least one digital signal processor may implement a digitalchannelizing receiver. A plurality of analog radio frequencyrepresentations within different radio frequency bands may be receivedthrough different antennas, and selectively concurrently switched to aplurality of channelizing receivers. At least one digital signalprocessor may comprise a channelizing receiver implementing at least onestage of digital down-conversion of a digital radio frequency signalfrom a frequency of the analog radio frequency representation to a lowerfrequency, while substantially retaining information modulated in theanalog radio frequency representation. A plurality of informationchannels may be extracted from the digital radio frequency signals.

A digital radio frequency signal may be cross-correlated and/orautocorrelated at the clock rate.

It is also an object to provide a method for receiving signals,comprising generating digital data directly from a received radiofrequency signal substantially without frequency translation, based on adigital data clock signal defined independently of the received signaland having a sufficiently high clock rate to preserve informationmodulated in the received radio frequency signal; and selectivelydirecting a plurality of sets of digital data and an associated digitaldata clock, to a plurality of digital signal processors, each acceptingthe generated digital data at the high clock rate. The selectivelydirecting may be non-blocking and multicasting.

An analog delay associated with a set of digital data and associateddigital data clock may be independently tuned with respect to other setsof digital data and respective associated clocks.

It is a further object to provide a receiver adapted to receive radiofrequency signals, comprising a plurality of digitizers, each adapted todigitize an analog radio frequency representation of each of a pluralityof radio frequency signals, without prior alteration of frequency, toproduce a respective plurality of digital radio frequency signals havinga respective associated radio frequency digital clock, the plurality ofdigital radio frequency signals having a sufficiently high respectiveassociated clock rate to preserve an information content of aninformation communication present in the analog radio frequencyrepresentation; and a switch matrix adapted to concurrently selectivelyswitch, based on an automated control signal, the plurality of digitalradio frequency signals and the associated plurality of digital radiofrequency clocks to a plurality of digital signal processors adapted toprocess representations of information contained in respective analogradio frequency representations.

The associated radio frequency clock for at least two of the respectivedigital radio frequency signals may be independent of each other and/orat different frequencies.

At least one associated radio frequency digital clock may have a clockrate above a Nyquist rate for a radio frequency carrier of the analogradio frequency representation. At least one associated clock rate maybe in excess of 1 gigahertz.

At least two digital signal processors may be concurrently switched toprocess a respective digital radio frequency signal.

At least one of the respective digital radio frequency signals maycomprise a parallel multiple binary bit digital representation of therepresentation of the analog radio frequency representation.

A delay matching element adapted to match a delay of a digital radiofrequency signal and respective associated radio frequency digital clockto maintain synchronization may be provided.

The switch matrix may dynamically route an analog radio frequencyrepresentation to a digital signal processor in real time. That is,while the receiver is receiving a signal, and without substantiallyinterrupting the reception and digital processing of the signal, aswitching state of the switch matrix may be modified. For example, anagile signal may be present in different bands, and therefore bereceived through different antennas over time. The switch matrix maytherefore switch the respective analog-to-digital converter feeding asignal to a respective digital signal processor in real time, to trackthe signal as it changes band, while maintaining a state of the digitalsignal processing chain. As necessary, a switching transient may besuppressed by a digital control signal, though this may not benecessary. On the other hand, a signal may change its modulation scheme,requiring a different types of processing, and therefore the signal froman analog-to-digital converter may be routed to different digital signalprocessors over time. Since there may be many different signals presentin each band, and each signal may require a different types ofprocessing, the system is preferably multicasting to permit multipledigital signal processors to receive the output of eachanalog-to-digital converter concurrently as may be required to processthe signals present. Therefore, preferably, the digital signalprocessors are capable of handling signals over a wide range of samplingrates, to allow such dynamic reconfiguration. The plurality of analogradio frequency representations may therefore be received throughrespective separate antennas, and at least two of the analog radiofrequency representations may be in different radio frequency bands.

At least one digital signal processor may implement a digitalchannelizing receiver. A plurality of analog radio frequencyrepresentations within different radio frequency bands may be receivedthrough different antennas, and selectively concurrently switched to aplurality of channelizing receivers. At least one digital signalprocessor comprises a channelizing receiver implementing at least onestage of digital down-conversion of a digital radio frequency signalfrom a frequency of the analog radio frequency representation to a lowerfrequency, while substantially retaining information modulated in theanalog radio frequency representation. At least one digital signalprocessor extracts a plurality of information channels from a respectivedigital radio frequency signal.

At least one digital signal processor may be adapted to cross correlateand/or autocorrelate a digital radio frequency signal at the clock rate.In the case of a single bit analog converter whose output is convertedto a multibit representation and the sample rate correspondinglyreduced, the cross correlation and/or autocorrelation may occur at thisreduced rate.

It is another object to provide a receiver for receiving signals,comprising a convertor adapted to generate digital data directly from areceived radio frequency signal substantially without frequencytranslation, based on a digital data clock signal defined independentlyof the received signal and having a sufficiently high clock rate topreserve information modulated in the received radio frequency signal;and a switch matrix adapted to selectively direct a plurality of sets ofdigital data and an associated digital data clock, to a plurality ofdigital signal processors, each accepting the generated digital data atthe high clock rate. The switch matrix may be non-blocking andmulticasting, and, for example, may be implemented as a Banyan networkconstructed from low temperature superconducting elements, such asniobium-based Josephson Junctions, to implement RSFQ circuits. At leastone tunable analog delay device may be provided adapted to tune ananalog delay associated with a first set of digital data and associatedfirst digital data clock independently of a delay associated with asecond set of digital data and associated second digital data clock.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of a multi-band, multi-channel RF transceiversystem incorporating an analog switch matrix as known in the prior art.

FIG. 1B is a block diagram of a multi-band, multi-channel RF transceiversystem incorporating a new digital switch matrix for use with digital RFarchitectures in accordance with one aspect of the invention.

FIG. 2 shows a basic digital switch using Josephson junctions.

FIG. 3A is a block diagram of a digital switch based on anon-destructive readout (NDRO) cell.

FIG. 3B is a schematic diagram of the digital switch based on anon-destructive readout (NDRO) cell.

FIG. 4 is a novel switch cell for routing clock and data together.

FIG. 5 is a block diagram of a 2×2 building-block for a 1:1 routermatrix.

FIG. 6 is a block diagram of a 4×4 switch matrix consisting of four 2×2building-blocks in a Banyan network.

FIG. 7 shows a block diagram of a multicasting switch matrix inaccordance with one aspect of the invention.

FIG. 8 shows an optional delay compensation network for a multicastingswitch matrix of the type shown in FIG. 7.

FIGS. 9A and 9B show implementations of a multicasting switch using RSFQcells, respectively with and without clock accompanying a data line.

FIG. 10 is a block diagram of a digital-RF switch matrix for receiversystems showing size of the switching array.

FIG. 11 shows a block diagram of a digital switch matrix included inboth receiver and transmitter of a complete digital-RF transceiversystem.

FIG. 12 shows a schematic diagram of a receiver.

FIG. 13 shows a flowchart for a receiver method.

DETAILED DESCRIPTION OF THE INVENTION I. Basic Switching Cells

RSFQ logic, first developed by Likharev, Semenov, and Mukhanov, is builtaround Josephson junctions (JJs), with lossless propagation ofsingle-flux-quantum (SFQ) voltage pulses, each corresponding to anintegrated pulse of 2 mV-ps. Two different types of RSFQ switch cellsare described, both of which are well known in the literature: the DCswitch and the NDRO switch. In either case, the general principle ofoperation is the same. A JJ is biased such that an SFQ pulse will causeit to temporarily exceed its critical current and then return to itsprevious state, thus emitting another SFQ pulse. The switching time,which depends on the critical current density (Jc) of the JJ, is about 2ps for the Jc=4.5 kA/cm². This ultrafast switching allows a very highrate (40 Gbps and higher) of SFQ digital signals. Whether or not aswitch responds to an input SFQ pulse depends on its designed controlconditions (DC bias, control current, or other concurrent digitalevents). For example, the state of the switch—whether it will pass orblock a digital input—may be controlled by the state of a coupledflip-flop, where control information could be stored.

FIG. 2 shows a schematic diagram of a simple DC-switch with only 2 JJs,which is controlled by applying DC current to the control line.

FIGS. 3A and 3B show another digital switch element, called anon-destructive readout (NDRO) switch, where the control information isstored in a reset-set flip-flop (RSFF). (The NDRO switch with 8 JJs ismore complex for a single switch, but is more easily scalable to largeswitch matrices.) An SFQ pulse applied to the Set input sets the RSFF tothe ‘1’ state. While it is in the ‘1’ state, any pulse applied to theinput will be read out as an SFQ pulse at the output synchronized to theclock input. This corresponds to the ‘ON’ (closed) state of the switch.

If a pulse is applied to the Reset input, the RSFF is reset to the ‘0’state. While it is in the ‘0’ state, any pulse applied to the input willescape through J6 and no SFQ pulse will be produced at the output. Thiscorresponds to the ‘OFF’ (open) state of the switch. One advantage ofthis type of switch is that only one external control line is requiredfor each cell to write the desired switch states for the entire matrix.Thus the control for the entire matrix can be stored as a serial digitalword. This is achieved by simply connecting the RSFFs of differentswitch cells as a shift register by applying the FF Out to the Set inputof the next RSFF.

One needs to route both data and clock from each input source throughthe switch to desired output ports, for fully asynchronous operation. Ofcourse, this can be accomplished by two switch cells which are manuallyset (reset) together. However a more elegant solution is part of oneaspect of the invention by routing the clock signal through an NDROswitch and controlling propagation of the data stream through an RSFF(see FIG. 4 where the clock line is shown as a dashed line), thusreducing the JJ count necessary.

FIG. 4 can be extended to accommodate a n-bit parallel data stream byreplicating instance of the Data RSFF for each bit stream of the n-bitparallel data stream, with each RSFF being reset by the clock outputsignal.

II. Routing Switch Architecture

Consider a switch architecture where each input is routed only to asingle output. (This constraint will be relaxed later.) To see how toscale up from a single switch, consider first a 2×2 building block (seeFIG. 5). This is done with 4 switch cells. The data and clock signalsfrom the first input are applied to Switch 11 and Switch 12respectively, and the data and clock signals from the second input areapplied to Switch 21 and Switch 22 respectively. The data and clockoutputs from Switch 11 and Switch 21 are merged (combined) at the firstoutput port, and the data and clock outputs from Switch 12 and Switch 22are merged (combined) at the second output port. We have shown bothclock and data paths, as well as the control (set) line, explicitly toillustrate the complexity of the design. We did not show the reset line,which will add to the routing complexity, but could be laid outsimilarly to the set lines in a way that should be obvious to oneskilled in the art. Throughout the layout, maintaining accurate relativetiming between paired clock and data signals is essential for correctoperation.

Once a 2×2 switching network is complete, standard network approachescan be used to generate larger networks. For example, FIG. 6 shows thedesign of a 4×4 switch using the well-known, scalable Banyan network,with the double lines indicating routing of both data and clock signalstogether.

III. Architecture of Multicasting, Cross-Point Switch Matrix

For some applications, it is necessary to copy one input to multipleoutputs, or vice versa. The relevant switch architecture here is an M×Ncross-point switch matrix that connects M inputs to N outputs (FIG. 7).Here each input propagates horizontally through a set of switch cells.If a switch is turned on, a copy of the input data stream is routed downthe corresponding column towards an output port; there is no degradationof signal quality since digital copying is lossless. Any number ofswitches may be turned on in each row to produce copies of the input atmultiple output ports. There is a potential problem of latency in thisstructure, since the signal propagation paths from an input port todifferent output ports is different. For most communicationsapplications, such small differences in propagation delays (a nanosecondor less) do not matter. Delay compensation networks (shown as trianglesin FIG. 8) can be added for applications, such as a network switch formultiprocessor supercomputers, that are sensitive to delay mismatches.Delay compensation can be achieved using passive lines of matchedphysical lengths or active transmission structures with matching delaytimes (such as tunable Josephson transmission lines).

We can use the same DC and NDRO switches (FIGS. 2 and 3 or the switchcell of FIG. 4) to build this multicasting switch matrix depending onwhether the clock line accompanies the data line. The building block ofthis matrix is a row (FIGS. 9A and 9B).

The multicasting switch matrix architecture in FIG. 7 is composed of M×Nswitches as in FIG. 3. Each switch has a set and reset line that permitsthe routing to be dynamically modified. For many implementations, assuggested in FIG. 9B, the “set” lines may be connected in series, andthe entire M×N array addressed by a single digital word. Given the veryfast clock speed, the entire array can be reconfigured in a short time.For very large arrays, partial parallel addressing (of separate rows,for example) may be used to speed up the reprogramming rate. In thisway, one may direct any input to any and all of the outputs, in a waythat is rapidly reconfigurable.

IV. Integration of Switch Matrix into Transceiver System

To exemplify the advantages of digital routing of RF signals, let usexamine the receive side in greater detail (FIG. 10). The analog RFinput signals are digitized directly at RF using an ADC behind eachantenna. Once the RF signals are in the digital domain, multiple copiescan be generated without compromising signal power and quality.Therefore, the digital-RF signal can be simultaneously applied to a bankof digital channelizing units, each operating independently to extract asubband from a wide input band. For a multi-band system, digitized datastreams from multiple ADC front-ends can be distributed to a bank ofchannelizers through a digital non-blocking, multicasting switch matrix.This architecture is scalable to an arbitrary number of channelizers (ormore general digital processors) and banded antenna-ADC pairs.Furthermore, the digital switch matrix can be programmed in real time todynamically reconfigure the communication system: changingband-to-channel allocation, cross-banding, etc.

In general, signal processing involves multiple steps, includingmultiple levels of channelization. For simplicity, here we haveconsidered only the first level channelization function: extraction of asub-band through mixing and filtering. This step requires digital-RFprocessing at clock speeds of 40 Gbps and beyond, and therefore, may beaccomplished using superconductor electronics.

One special requirement for the switch matrix is its ability to supportmultiple input data rates. The ADCs may not share the same clockfrequency. For example, the choice of clock frequency may depend on thecenter frequency of the band for convenient digital in-phase andquadrature (I & Q) mixing, which requires the clock to be 4 times higheror multiples thereof. An asynchronous or better-said multi-synchronousswitch, routing both the clock and digitized data together, is essentialto address this requirement. This ability to distribute digital signalswith several different clock frequencies simultaneously within the samegeneral-purpose switch matrix is a unique feature of one aspect of theinvention.

A general block diagram of a complete direct digital-RF communicationsystem is shown in FIG. 11. A multi-band RF communication systemconsists of an antenna subsystem to capture electromagnetic energy indifferent RF bands and a transceiver subsystem to transmit and receiveinformation from each RF band through a variety of signal processingsteps (e.g., up/down-conversion, filtering, modulation/demodulation,coding/decoding, etc.). The goal is to dynamically assign the availablesignal processing resources to the input bands to meet the communicationneeds. This requires dynamic RF distribution and routing. The top halfof FIG. 11 shows the receive side, where direct digitization of RFsignals by analog-to-digital converters (ADCs) is followed byprogrammable digital routing to a bank of digital processing units. Thebottom half shows the reciprocal transmit side. Here, multiple transmitsignals are digitally synthesized and connected to digital-to-analogconverters (DACs), coupled to digital-RF predistorters that linearizethe RF transfer function of high power amplifiers (HPAs) directly.

A similar switch matrix may also be incorporated within a digital-RFtransmitter system. In one embodiment of the invention, as indicated inthe Multicasting Switch Matrix in FIG. 7, it may be desirable to directmore than one digital-RF input to be combined in the same output.Functionally, the multiple inputs may be added in a Combiner circuit,where this must be carried out in the Digital Domain in the digital-RFsignals. Let us assume here that the clock frequencies of these signalsto be added are the same. That is generally the case for signalsdesigned for transmission using the same output antenna, which arewithin the same output band. Then the Combiner circuit can beimplemented as simply a fast clocked Binary Adder, as has already beendemonstrated in RSFQ technology. The outputs of the Binary Adder circuitmay be passed along to a multi-bit Digital-to-Analog converter (DAC),the output of which can then be passed to an RF Power Amplifier, andthen to a Transmission Antenna.

FIG. 12 shows a receiver system in which a plurality (m) of analogsignal couplers ASC₁ . . . ASC_(m) each provide an analog radiofrequency signal to a respective analog-to-digital receiver ADC-1 . . .ADC-m, each of which provides an input to a switch matrix, having switchelements s₁₁ . . . s_(mn). A plurality (n) of digital signal processorsDSP₁ . . . DSP_(n) receive outputs from the switch matrix, and processthe received digitized signals. The switch matrix is non-blocking, and,not shown in the figure, multicasting, so the number of digital signalprocessors may be the same or different than the number ofanalog-to-digital converters.

FIG. 13 shows a flowchart of a method according to the presentinvention. Initially, m analog RF Signals are rapidly sampled inparallel 1301, generating m oversampled digital signals, each with anassociated clock. The m digital signals (each with clock) are coupled torespective inputs of an m×n digital RF Switch Matrix 1302, whichregenerates n digital outputs and associated clocks, where m and n maybe different. Switches for a desired routing may be activelyreconfigured, in parallel and/or serial fashion 1303. Outputs of theswitch matrix are then coupled to an array of n Digital RF SignalProcessors 1304. Parallel digital signal processing is used fordownconversion and extraction of at least one digital baseband signalfrom each digital RF signal 1305.

While various embodiments of the present invention have been illustratedherein in detail, it should be apparent that modifications andadaptations to those embodiments may occur to those skilled in the artwithout departing from the scope of the present invention as set forthin the following claims.

What is claimed is:
 1. A method for receiving a radio frequency signal,comprising: digitizing, without prior alteration of frequency, an analogradio frequency representation of each of a plurality of radio frequencysignals to produce a respective plurality of digital radio frequencysignals having a respective associated radio frequency digital clock,the plurality of digital radio frequency signals having a sufficientlyhigh respective associated clock rate to preserve an information contentof an information communication present in the analog radio frequencyrepresentation; concurrently switching the plurality of digital radiofrequency signals and associated digital radio frequency clock to onesof a plurality of digital signal processors; selectively automaticallycontrolling the concurrent switching of a plurality of digital signalsand associated digital clock to the respective plurality of digitalsignal processors; and producing, by the digital signal processors,processed representations of information contained in respective analogradio frequency representations.
 2. The method according to claim 1,wherein the associated radio frequency clock for at least two of therespective digital radio frequency signals is independent.
 3. The methodaccording to claim 1, wherein at least one associated radio frequencydigital clock has a clock rate above a Nyquist rate for a radiofrequency carrier of the analog radio frequency representation.
 4. Themethod according to claim 1, wherein at least one associated clock rateis in excess of 1 gigahertz.
 5. The method according to claim 1, whereinat least two digital signal processors are concurrently switched toprocess a respective digital radio frequency signal.
 6. The methodaccording to claim 1, wherein at least one of the respective digitalradio frequency signals comprises a parallel multiple binary bit digitalrepresentation of the representation of the analog radio frequencyrepresentation.
 7. The method according to claim 1, further comprisingthe step of matching a delay of a digital radio frequency signal andrespective associated radio frequency digital clock to maintainsynchronization.
 8. The method according to claim 1, further comprisingthe step of selectively controlling a delay of a digital radio frequencysignal.
 9. The method according to claim 1, further comprising the stepof generating at least two of the associated radio frequency digitalclocks having different frequencies.
 10. The method according to claim1, wherein a switching occurs to change an analog radio frequencyrepresentation routed to a digital signal processor dynamically in realtime.
 11. The method according to claim 1, wherein the plurality ofanalog radio frequency representations are received through respectiveseparate antennas.
 12. The method according to claim 1, wherein at leasttwo of the analog radio frequency representations are in different radiofrequency bands.
 13. The method according to claim 1, wherein at leastone digital signal processor implements a digital channelizing receiver.14. The method according to claim 13, wherein a plurality of analogradio frequency representations within different radio frequency bandsare received through different antennas, and selectively concurrentlyswitched to a plurality of channelizing receivers.
 15. The methodaccording to claim 1, wherein at least one digital signal processorcomprises a channelizing receiver implementing at least one stage ofdigital down-conversion of a digital radio frequency signal from afrequency of the analog radio frequency representation to a lowerfrequency, while substantially retaining information modulated in theanalog radio frequency representation.
 16. The method according to claim1, further comprising the step of extracting a plurality of informationchannels from the digital radio frequency signals.
 17. The methodaccording to claim 1, further comprising the step of cross correlating adigital radio frequency signal at the clock rate.
 18. A method forreceiving signals, comprising: generating digital data directly from areceived radio frequency signal substantially without frequencytranslation, based on a digital data clock signal defined independentlyof the received signal and having a sufficiently high clock rate topreserve information modulated in the received radio frequency signal;and selectively directing a plurality of sets of digital data and anassociated digital data clock, to a plurality of digital signalprocessors, each accepting the generated digital data at the high clockrate.
 19. The method according to claim 18, said selectively directingis non-blocking and multicasting.
 20. The method according to claim 18,further comprising the step of independently tuning an analog delayassociated with a set of digital data and associated digital data clock.